Cockpit lighting can interfere with the optimum operation of night vision apparatus such as a night vision goggle, in several specific ways. For each interference mechanism, the effect on the image seen through the night vision apparatus is to reduce the light level or contrast of the useful image (the view from outside the aircraft). This reduction in light level or contrast can be manifested as a reduction in visual acuity and/or as an observed loss of contrast or brightness. In order to determine if a particular configuration of cockpit lighting or instrument illumination interferes with the proper operation of night vision apparatus the arrangement of the present invention can be used to implement a night vision apparatus visual performance assessment procedure such as is described in APPENDIX C of the present document. Although visual evaluation of night vision apparatus output by a human operator is most readily accomplished other night vision apparatus output evaluation apparatus may be used within the scope of the present invention.
Currently, United States military personnel use the U.S. Air Force Resolution Chart shown FIG. 5 herein when performance evaluating or adjusting night vision apparatus. This resolution chart is now a standard for use by U.S. and allied military units performing night vision apparatus missions. This chart has a series of increasingly finer pairs of black and white bars, bars that, when viewed through night vision apparatus, allow maintenance personnel to evaluate and adjust the viewed image quality and allow the war fighter to personally perform night vision adjustments such as objective lens focusing, interpupillary distance selection, tilt angle adjustment, eyepiece selection and battery checking prior to a night vision mission. The resolution chart of U.S. Pat. No. 4,607,923, issued to Task et al. in 1986 and other resolution charts as described later herein may also be used for these purposes.
Use of such resolution chart for the present night vision apparatus visual performance assessment or other purposes however requires it to be precisely irradiated at low light levels, levels on the order of 0.0025 foot-lamberts for example. Such irradiance levels afford almost no human vision capability. This chart usage irradiance is often accomplished with the aid of an irradiance-measuring instrument such as a photometer or a radiometer or the low level instrument described in the U.S. Pat. No. 7,235,779. Photometer and radiometer instruments however range in value from $5,000 to $28,000 or greater as may be observed in the catalog or on the web site of one supplier of such instruments, Hoffman Engineering Corporation of Stamford, Conn., http://www.hoffmanengineering.com. Such instruments are also generally unsuited for use under field conditions as is dictated by their cost and their substantially fragile nature.
The present invention is believed to provide an answer for these difficulties in addition to providing night vision apparatus visual performance assessment.
The U.S. Pat. No. 4,607,923, U.S. Pat. No. 7,235,779 and each other patent document and reference document identified herein are also hereby incorporated by reference herein.